Tips/tricks/observations on me mini mill

[rashid11]

I am talking about $495 mini mill sold by numerous outfits
here in US: HF, Grizzly etc.


- Use the X-Y clamps: every now and then when
taking an unavoidable heavy cut, the chatter will be
pretty bad - the mill is simply not rigid enough. Lead screws flex
quite a bit, even when you manage to lower the backlash. I found that
by tightening the direction-of-the-cut clamping handle to where one can barely
move it with handwheel helps a whole lot - cuts that seemed
unattainable were possible.


- speaking of the locking handles: they are pretty bad and strip
easily. I ordered replacement from McMaster (6mm) and these are
rock solid. Replace all three: XYZ


- The sliding Z-stop thingy is weak - be careful not to overtighten
it, as it will snap right down the middle. And when it does you will
see that it is made
of graphite-like material. I recommed milling your own -when and if you
break the stock one.


- Be careful as you slot: if you use centercutting end mill and heavy
cuts, it will tend to pull the Z down and ruin that tenths precision
you were aiming for. Lock the Z, pull up the sliding Z stop and lock
that
one too. Check often. Use non-center-cutting end mills (4 flutes are
mostly non CC but make sure by checking )


- I did the drive belt mod on mine a while back (not the HA one, but
the one that eliminates all and any gears between the motor and the
spindle). I love it . Highly recommended.


- Surface grinding on cheap: a while back while visiting a local store
I mentioned small grinding stones mounted on cheap adapter, with 1/4"
shank - for something like $2, in various D (2"-3") and thickness (1/4 and up). I picked up
a few. Mount diamond dresser into the vise (use horizontal Vee grove),
mount the stone, get it so that the diamond is on the
stone's center line with some separation (check for that by manually
rotating the spindle). I personally use X feed to drive the stone into
the diamond. Start up, feed the stone to where it barely touches, use Z
to move the stone up/down, crank up the RPMs. Feed another thou and
repeat. Stop and check for nicely trued up stone. If you are not
wearing a respirator mask and safety goggles when doing it, you should
not be allowed anywhere near the machinery.


Abrasive dust will be all over the mill as you do it. I found that
wrapping most of the surroundings into the common kitches alum foil
helps to keep the debri out. Shop vac is a must - afterwards for sure,
better yet right during the process.


- Examples of surface grinding : I trued up my chuck's jaws, made my
own T-slot cutter out of $2 end mill (see below).


- T-slot cutting. I built a t-slotted cross slide for my mini lathe
(out of CRS, CI is just too darn expensive !!!) When preparing for
T-slotting I milled the required depth/width of the slot for the
T-cutter's neck. As I started mounting 5/16 t-cutter, I could not help
but notice just how much metal will need to removed by the said cutter
in a single pass. 1/4" high cut, with .100 or so on ea side.


Naturally it simply doesn't work - unless you're ready to feed in at
1 thou/month rate. The noise will wake up dead in nearby cemeteries.
The chatter will get a 1000 lb bench to tap dance all over one's shop.
Aborted - after trying every possible RMP/feed rate in both
feed directions.


I decided to make my own T-slot cutter out of 4-flute mill ( I bought a
20-piece set for $30 a long while back, TIN coated HSS variety). I got
one with the D almost equal to the required width of slot (may be 20
thou
under). MOunted it into my vise's vertical v-grove. Installed the
el-cheapo grinder stone. Arranged the hight to make 1/8 high cutting
head,
lock the Z. We make it thin to reduce the amt of material it removes in
a single pass.


Feed the mounted end mill into the stone for required depth, nice and
slow, back out,
loosen the vise, turn the end mill 30 degrees or so , repeat. in 5 mins
you should have the cutter that works . The neck doesn't have to be
perfectly concentric or round, for that matter. Of course, make sure
it is narrow enough to enter the slot. Rest the butt of the end mill
on a parallel, to keep it on the same height.


Another way to make the same thing in a much prettier way is to use
tool post grinder on a lathe. Dremmel-like tool can be epoxied/bolted
onto 3/8-1/2 sq shank (Varmint Al's idea), to be mounted in a toolpost
of your choosing. Use 3/4-1" OD slim grinder stone for best control.


To use the cutter: cut the slot in 3-4 passes. First one will be full
height worth of metal removal, so tighthen the feed's handle - see
above. Go slow, subsequent passes you
can make easier by removing smaller amt of metal. Finish the slot with
the real T-slot cutter - it will clear it all up to right height, width
and make the shoulder square.


- Make your own DRO for the mill - shumatech.com way. For $150 or so
you will get a complete DRO that will rival commercial ones selling for
20x the amount. Can save some money by using HF's calipers for
scales.


- Swarf containment is rather important for an HSM. I bought a roll of
transparent film @ local hobby shop, in .010 thickness. Cut a strip
of the right height for the particular, messier cut you're taking.
Wrap it around the head assembly, as close to 360 as possible, so that
the edge of the film touches
the work's surface. I use pieces of alum sticky tape to temporarily
hold the thing in place. It removes easily and doesn't leave any
residue.


As you cut, the film will contain the chips to the work's area, so stop
the cut every now and then and clean up. Still better than having to
shop vac the whole shop. I dispose of the film agfterwards - as it is
covered in chips and cutting oil and is not transparent anymore.


- On the same subject: the shoes you wear in the shop should not be
allowed back in the house. As simple as that. Use old ones or buy
a pair of el cheapo ones. I wear ... drum roll .. sandals. The boots
are no go as the chip will fall in with no way to get out. With sandals
it is easy to keep the chips out even though they are open type. I
stick the shop vac nozzle into the front opening after most heavy cuts
to vacuum whatever got it. What you don't want to happen is for a
splinter to go in and then break off.


Before you start a cut, make sure the toes are not sticking in the
open. Use longer apron, stick the belly out


- On somewhat related: make your own aprons out of synthetic cloth
they sell @ HD to protect furniture when painting (egg-shell smooth
on one side with textured bluish opposite side). Cut to length/width,
round off the top part, cut a half-a-circle hole on top for the head.
Cut 2 holes waist-high on the sides and put some kind of straps in.
Should not take you more than 1 min to make one.


Wear it with textured, cotton-like side _in for comfortable feel, with
smooth side out. Works real nice, chips just slide down the smooth
exterior, never ever stick on. Cut few aprons in dift length.
Wear short ones on a hot day when working with wood. Longer ones are
better for metal - especially when they reach all the way to your toes.


Discard when they get dirty. A roll of that cloth will last you a
century or so.


I never put any pockets on it - this is where the chips will end up
just waiting for you to stick your fingers in.


- On cooling: Like quite a few of fellow HSMs I work out of my attached
garage. Used to get quite uncomfortable in the summer (NJ) when I could
not even work in there. I could not mount regular AC in there (it is a
townhouse). Last summer (late enough for a sale) I got me a portable
upright AC @ HD. This one exhausts the heat through 4" flex pipe. Stick
the pipe outside and you're in business.


- for face milling - get import face cutting carbide insert mill from
Grizzly or similar. They cut ANYTHING, are accurate and cheap enough
these days. Make sure the column is indicated in for a nice flat cut.
Watch the patterns formed on the surface as you cut - it is
very easy to tell when the column is not true. When you manage to dull
the insert, rotate it to expose the next tip and continue. Inserts are
very cheap.

[RotarySMP]

Great post of helpful hints and tricks. Thanks.